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"Typically around one third of people who fall ill with listeriosis die every year. Most of the cases are never related to an outbreak like this one we're seeing with the rockmelon contamination," she said.

Listeria is a commonly found bacteria and for many people who consume foods that contain it, it does not cause illness. But it can pose a threat to the elderly, pregnant women or those with conditions like diabetes or cancer.

Listeriosis begins with flu-like symptoms including chills, fever and muscle aches. It has an incubation period of up to 70 days.